Is ERMI an official EPA-approved home mold test?

No, and this is the single most misrepresented fact in the mold industry. EPA scientists developed the ERMI methodology and it has been peer-reviewed for research applications, but EPA has not validated it as a diagnostic tool for assessing an individual home. Companies that market ERMI as an 'EPA-certified' pass/fail home test are overstating what the agency has actually said about it.

Should I get an ERMI test instead of standard air sampling?

They measure different things and answer different questions. Standard air sampling (spore trap analysis, compared against an outdoor control) tells you what's aerosolized right now. ERMI and HERTSMI-2 analyze settled dust via qPCR DNA analysis, which captures a longer history of what's been present in the space — including species that don't aerosolize easily, like Stachybotrys. A thorough assessment often uses both, not one instead of the other.

What's a 'good' ERMI or HERTSMI-2 score?

ERMI scores are typically reported on a scale where values at or below 0 are broadly consistent with homes without a history of water damage, and rising positive values correlate with increasing mold burden — but there's no single EPA-sanctioned numeric cutoff that applies uniformly to every home, climate, and construction type. HERTSMI-2 is more commonly used with a specific post-remediation clearance threshold, which your assessor should explain in the context of your specific report rather than a generic number quoted online.

ERMI and HERTSMI-2 Explained: What DNA-Based Mold Testing Actually Measures

Homeowners researching mold increasingly come across “ERMI” and “HERTSMI-2” — DNA-based tests that sound more rigorous than a standard air sample, and that’s a reasonable instinct. But a lot of what’s published about them online either oversells what they prove or gets the underlying science wrong. This is our attempt to explain both precisely, including the caveat most companies leave out.

What these tests actually measure

Standard mold air sampling uses a spore trap: air is pulled through a device that catches airborne particles on a sticky surface, which a lab then examines under a microscope and counts by species, always compared against a simultaneous outdoor control sample. It tells you what’s aerosolized in that specific moment.

ERMI and HERTSMI-2 work completely differently. Both analyze a dust sample — typically collected with a specialized vacuum sock from carpet, upholstery, or other settled-dust surfaces — using quantitative PCR (qPCR), a DNA-amplification technique that detects and quantifies the genetic material of specific mold species, whether or not those species are currently airborne. Because dust accumulates over time, this approach can pick up a longer history of mold presence in a space, including species like Stachybotrys chartarum that don’t aerosolize readily even when present on a surface — one reason surface and dust-based testing matters alongside air sampling when Stachybotrys is a real concern, not just an assumption.

ERMI: what it is, and what EPA actually says about it

ERMI was developed by EPA researchers as a research tool: the qPCR results across 36 specific mold species are combined into a single index score meant to give researchers a standardized way to compare mold burden across homes in epidemiological studies. It’s been peer-reviewed and published in research contexts.

Here’s the part that matters and that a lot of marketing leaves out: EPA’s own position is that ERMI has not been validated as a diagnostic tool for assessing an individual home. It was built to compare populations of homes in research, not to hand a single homeowner a pass/fail number. That doesn’t make ERMI useless — a qPCR-based dust analysis genuinely adds information a spore trap alone won’t catch — but a report that presents a single ERMI number as an authoritative, EPA-certified verdict on your specific house is overstating what the science actually supports. We’d rather tell you that plainly than let an impressive-sounding number stand in for a proper assessment.

HERTSMI-2: the faster, narrower version

HERTSMI-2 uses the same qPCR dust-sampling method as ERMI but analyzes only 5 species considered highest-risk (including Stachybotrys chartarum and Aspergillus versicolor), rather than the full 36-species panel. That narrower scope makes it faster and less expensive to run, which is why it’s more commonly used as a post-remediation clearance check — a quick way to confirm a space that’s just been remediated doesn’t show elevated levels of the species most associated with chronic water damage, before it’s re-occupied.

How we actually use this science

Air sampling with an outdoor control remains the baseline for identifying an active, current airborne mold problem — it’s fast, well-established, and directly comparable to a “normal background” reference.
Surface sampling (tape lift or swab) confirms what’s actually growing on a specific visible area, which air sampling alone can miss for less-aerosolizing species.
qPCR dust analysis (ERMI/HERTSMI-2) adds a longer-history, DNA-based layer — most useful either as a research-grade supplement to a broader assessment, or specifically as a HERTSMI-2 clearance check after remediation, not as the sole basis for a diagnosis.
Independent, third-party testing — regardless of which method is used, whoever tests should not be the same crew doing the remediation. That’s not specific to any one test type; it’s the conflict-of-interest safeguard that matters most.

What we’d tell anyone quoted an ERMI test as a diagnosis

If someone hands you a single ERMI number and calls it a definitive diagnosis of your home, ask what it’s actually being compared against — and ask directly whether they’re aware that EPA itself doesn’t endorse ERMI for that specific use. A qPCR dust analysis is a genuinely useful piece of evidence. It’s not, on its own, the whole picture, and anyone telling you otherwise is selling you certainty the science doesn’t actually offer.

[Sources: U.S. EPA, Environmental Relative Moldiness Index (ERMI) — epa.gov/air-research/environmental-relative-moldiness-index-ermi; peer-reviewed ERMI validation literature, National Institutes of Health PMC.]